Radio receiving circuits



Feb. 16, 1932, H. T. FRHS RADI O RECEIVING CIRCUITS Filed Nov. 1, 1924 //7 yen/0r Ham/0 Z' fins by my HARALD r. FRIIS, or RED BANK, PANY, INCORPORATED; on NEW YORK,

' hereto.

Patented Feb. 16, 1932 UNITED STATES; PATENT OFFICE N EW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COM- N. Y., A CORPORATION OF NEW YORK RADIO RECEIVING CIRCUITS Application filed November circuits embodying intermediate frequency amplification and more particularly to balancingcondenser circuits for use in connection with intermediate frequency amplifiers.

An object of the invention is to prevent feed-back in' an intermediate frequency amplifier containing space discharge-devices due to the internal'capacity of said device s. 7

Another object of the invention is to, reduce the number of circuits necessary to balance the internalcapacity of a, plurality of vacuum tubes.

A feature of the invention is an intermediate frequency amplifier comprising a plurality of tubes coupled by tuned circuits in which feed-back is prevented by balancing condensers connected from a common point on a tuned coupling circuit to the grid and plate respectively of two successivetubes.

In high frequency amplifiers feed-backcan be more effectively prevented when timed circuits are used to couple successive tubes'than when transformer couplings are used due to the distributed capacity of the transformer ,wlndings which tends to make the circuit untermediate frequency amplification frequently oscillate unless the tuned circuits are un-- balanced or a potentiometer added which Inaterially reduces the efficiency. By means of this invention intermediate frequency amplifiers are prevented from oscillating under any condition of adjustment, making the circuit more stable and dependable and easier to manipulate. v e I The novel features which are believed to be characteristic of this invention will be pointed out with particularity in the claims appended This invention, however, as to its object and advantages the details of I its organization and its manner of operation will be better understood by referring to the following specification taken in connection with the accompanying drawings forming a part thereof in which: V a a r Fig.1 illustrates a radio receiving circuit 1, 1924. Serial No. 747,167.

containing an intermediate frequency amplifier embodying this invention.

Fig. 2 shows a modification of that portion of the circuit of Fig. 1 between the lines 11 and 2-2. j

Referring to the drawings in detail,'Fig. 1 shows a double-detection receiver" comprising a tuned loop circuit consisting or loop 1 and variable tuning condenser 2. This loop circuit is connected tothe first detector 3 upon the grid of which hi hfrequency oscillations are impressed by means of the oscillator O and coil 4. The high frequency oscillations from oscillator O combine with the incoming carrier waves to produce a wave whose frequency is equal to the difference of the frequencies of the two applied waves. The frequency of the wave thus produced is termed the intermediate frequency. The plate circuit of tube 3 is connected to filter 5 which is designed to pass only the intermediate frequency currents. This filter may be of any suitable type, several being shown and described in U. S. Patent to Campbell 1,227,114, May 22, 1917. Intermediate frequency, currents passedby filter 5 are impressed upon intermediate frequency amplifier B by means of transformer 6.

Intermediate frequency amplifier B consists of tubes 7 and 8 coupled by a tuned circuit comprising condenser 9 and series coils 10 and 11 which are electrically equal and equivalent. The plate circuit of tube 7 is connected across coil 10 which is in turn connected to the grid circuit of tube 8. Balancing condenser 12 which is equal in capacity .to the internal capacity of tribe?" is connected between the grid of tube 7 and the terminal is of coil 11..- Balancing condenser 13 is connected from terminal 14 of coil 11 to the plate of tube 8. v In-the operation of the system, potentials which are impressed across coil 10 will be repeated and amplified by tube 8. Any tendency to oscillate, however, will be prevented by impressing upon the grid of tube 7 a potential from terminal 14: of coil 11 through condenser 12 equal and opposite to that inipressed' by the upper terminal of coil 10 through the internal capacity of the tube.

In a similar manner equal and opposite potentials are applied to the plate of tube 8 which will neutralize the tendency to set up sustained oscillations as a result of the inherent feed-back coupling within the tube 8.

The current output of this intermediate frequency amplifier is passed through a detector D and audio frequency amplifier A, if desired, from which it may be taken to a loud talking device or head phones E for reception.

In the modification shown in Fig. 2 tubes 7 and 8 are loosely coupled by tuned circuits 9, 10, 11 and coupling condenser 15 which may be variable. The balancing condensers in this case are taken from the terminals 1d of coils 11 in the same manner as shown in Fig. 1 and operate in the same manner. Space current is applied to the space discharge devices in the circuit shown in both figures by battery 16.

Any tendency for the intermediate frequency amplifier to oscillate is eliminated by this invention with the use of only one tuned coupling circuit for each two tubes in the amplifier. This reduces the number of tuned coupling circuits required and the 'difiiculty of assembling and adjusting. While only two tubes have been shown the system is equally applicable to an amplifier comprising any even number of tubes employing tuned circuit coupling.

Although the invention has been shown and described as applied to particular circuits it is not limited thereto but is of general application and should only be limited in scope as defined in the following claims.

What is claimed is:

1. In an amplifier comprising three-element space discharge repeaters each having input and output circuits, coupling means for connecting the output circuit of the first repeater with the input circuit of the second repeater, means comprising balancing circuits having impedance elements therein for preventing feedback in said repeaters, said balancing circuits being respectively connected from the grid of the first repeater to said coupling means and from the coupling means to the plate of the other repeater.

2. An amplifier system comprising a plurality of three-electrode space discharge devices in tandem, said devices having an inherent tendency to produce oscillations such, for example, as that due to internal capacity, a coupling circuit between two of said devices, and a plurality of condensers for counteracting the inherent tendency, said condensers each having one terminal connected to the same point on said circuit electrically opposite to the grid and plate connection and the other terminals respectively connected to the grid of the first device and the anode of the other device.

3. In a radio receiving circuit, means for amplifying signaling waves comprisin space discharge repeaters having grids an plates and a tuned coupling circuit therefor, and means for preventing feed-back in said space dicharge devices comprising balancing condensers connected between a point on said tuned coupling circuit electrically opposite to the grid and plate connection and the grid of one repeater and the plate of another of said repeaters.

4. In a radio receiving circuit, means for amplifying oscillations comprising space discharge repeaters having grids and plates and a tuned coupling circuit therefor, and means for preventing feed-back in said space discharge devices comprising balancing condensers connected between a point on said tuned coupling circuit electrically opposite to the grid and plate connection and the grid of one device and plate of another device respectively.

5. In a radio receiving circuit, space discharge repeaters having grids and plates for amplifying oscillations, tuned coupling circuits for said space discharge repeaters, means connecting said tuned circuits with the plate and grid respectively of two successive repeaters, means for passing said oscillations through said repeaters and preventing the passing of oscillations of all other frequencies, and means for preventing feed-back in said repeaters comprising balancing condensers connected around said repeaters to a point on said coupling circuit electrically opposite to the grid and plate connection.

6. In a high frequency amplifier, a plurality of space discharge tubes each having input and output circuits, a tuned coupling circuit, said tubes being coupled in tandem by said circuit, and means for balancing the circuits connected to said coupled tubes, for the prevention of inherent oscillations, comprising separate paths between a point on said coupling circuit electrically o posite to the grid and plate connection and the grid of one tube and anode of the other tube, said paths containing reactive devices.

7. In an amplifier system, a plurality of three-electrode space discharge tubes, a resonant coupling circuit, said tubes being coupled in tandem by said circuit, and separate paths between a point on said resonant circuit electrically opposite to the grid and plate connection and an anode of one tube and a grid electrode of another tube, said paths including condensers for supplying reaction efiects reverse to those supplied b inherent capacity between electrodes of sai tubes for preventing inherent oscillations.

8. In an amplifier system, a plurality of three-electrode space discharge tubes each having input and output circuits, a resonant circuit for coupling the output circuit of the first tube with the input circuit of the second tube, and separate balancing circuits between a point on said resonant circuit electrically opposite to the grid and plate connection of the tubes and a grid element of one tube and the anode ofanother tube.

In Witness whereof, I hereunto subscribe my name this 27th day of October, A. D. 1924.

HARALD TQFRIIS. 

